The disk space on your storage system is divided into two portions. One portion is for shared folders; the other is for backups of your computer disks. You can expand the amount of disk space allocated for shared or home folders later as long as free disk space is available, but you cannot reduce it without reconfiguring your disks and losing all your data.
See the section on Expanding the Shared Storage in the Intel® Entry Storage System SS4000-E User guide.
That might give you the free space you need to access the shared folder.
Unfortunately, there's no free space on the drive and no folders to delete other than Home and Public, which can't be deleted.
If I were to replace a drive with a larger drive, let the array rebuild, then replace a second and let the array again rebuild, etc. until I had four larger drives in the box, could I then extend the array and get space?